>327k '94 Ford Escort 4 door sedan 1.9L SOHC. The Rusty Reaper forced me to replace it. Drivetrain was still at least 90%.
Our user manual warns against shutting the engine down during a rev... that we wait until it returns to idle RPM. This is to protect the turbo. I've witnessed the hang and it's by design; theoretically to protect the turbo. Get in it HARD and just as it starts to kick in, get off the accelerator and clutch in. I've seen my RPMs start to go down then the ECU immediately revs it back up and hangs it there. It's an incredibly rare occurrence for me. It's never interfered with my driving, has never lasted more than a couple of seconds and isn't a problem to me. I'd rather the ECU do that, than prematurely wear out the bearings on my turbo.
Sorry to disagree with you both, but Rev Hang exists and it is for emissions, not turbo.
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Recently, manufacturers have been intentionally implementing rev hang within ECU programming to save themselves from a potential emissions scandal. When the throttle is released and the clutch is dipped, an ECU with rev hang is programmed to leave the throttle slightly more open than usual.
This strategy is used because it was found that suddenly closing the throttle produced a sudden spike in gas pressure within the crankcase which emphasised the rate of oil vaporisation, thus adding to emissions from the engine. Also, when the throttle is suddenly shut, the fuel mixture suddenly becomes lean which creates NOx (oxides of Nitrogen) which also contributes to emissions.
By keeping the throttle open for a small period of time after the pedal had been released, this pressure spike was avoided and cleaner emissions were achieved. Found most prominently in US-spec vehicles to meet the emission rules over the pond, this pre-programming has frustrated many owners since its development. Rev hang can even be found in Subaru’s WRX STI, along with prominent cases in VW and Hyundai products.
To help eradicate this high pressure within the crankcase, a PCV (positive crankcase ventilation ) valve is used which can reduce the need for a rev hang system when fully functioning. This PCV valve is used to regulate the pressure within the crankcase that can fluctuate to high levels when gear changes occur. In internal combustion engines, it is inevitable that a small amount of ‘blow-by’ occurs, which is when gases from the combustion chamber seep past the piston rings and travel down into the crankcase. The job of a PCV valve therefore is to remove a proportion of the blow-by fumes away from the crankcase, thus reducing the amount of high pressure gas contained within.
Although an intentional rev hang system would go a long way in saving your oil levels and help your car sail through an emissions test, most petrolheads only see it as a hindrance to their driving pleasure. With a quick reprogramming of the throttle body control codes and a bit more competence when it comes to checking oil levels, rev hang can be eradicated and your gear changes can be as smooth and as quick as you desire.
https://www.carthrottle.com/post/rev-hang-explained-and-why-petrolheads-hate-it/